It’s January and I’m heading to a farm call. When I arrive, the cow is down and already aborted a fetus.
The farmer smiles at me and says, “you’d better check to make sure she doesn’t have another one, since you’re already here.”
I observe the size of the cow and I’m acutely aware of the diminutive length of my arms. One advantage to being petite is I can use both arms to manipulate a fetus while my more substantial colleagues are limited to one arm at a time.
Half an hour later, the cow is in the barn’s head gate. I’m up to my left armpit and sure enough, I feel another set of feet. As I check for orientation, I consider possible reasons why this cow was aborting.
At about five months gestation, the cow is considered to be in the second trimester. Most abortions previous to this gestational age go unnoticed and turn up as open cows.
Cows abort for many reasons: infectious agents, toxins, stress and congenital malformations.
As a diagnostic pathologist in training, I am most likely to see cases of infectious abortion submitted to the diagnostic lab.
Obvious congenital malformations such as inside-out calves, while interesting, are less likely to be submitted because the cause is obvious and they tend to affect individuals rather than the herd.
In cases of multiple abortions, close co-operation between the producer, veterinarian and pathology lab are necessary to reach a diagnosis.
If submitting samples to the lab, it is important to provide the most complete, fresh fetus possible. In abortion outbreaks, submitting multiple fetuses also increases the chance of a diagnosis.
The placenta is another essential component. Some infectious causes make only detectable changes in the placenta. While a whole placenta is best, even portions can sometimes provide the necessary sample for detecting the cause.
Freeze the fetus and placenta if there is a significant delay between when they are discovered and when they are submitted. This prevents the tissues from rotting and environmental bacteria from overgrowing. Producers should do this even if they aren’t sure at first if they will pursue diagnosis.
Provide the following information with the samples: number of abortions, herd size, feed type, vaccination history, approximate gestational age, whether it is cows, heifers or both affected, are placentas retained and are the aborting females sick.
The exact cause of infectious abortions are rarely seen with the naked eye during an autopsy, but collecting bacterial cultures and tissue samples for microscopic examination increases the chance of determining the source of abortion.
Many tissues are searched for signs of disease under the microscope, such as pus, bacteria, dead cells and fungi.
Based on this information, bacterial cultures and tests for diseases such as bovine viral diarrhea can be done to nail down the cause. Once a diagnosis has been reached, management interventions such as vaccinations can be implemented.
Back in the barn, I applied the calving chains and extracted the second fetus. The cause of abortion was not determined in this cow and luckily it was the only one in the herd to abort that year.
I can’t emphasize enough that if you find an aborting cow, save the placenta, too.